Bright, single helicity, high harmonics driven by mid-infrared bicircular laser fields.

Area of Science:

• Atomic, Molecular, and Optical Physics
• Attosecond Science
• X-ray Spectroscopy

Background:

• High-harmonic generation (HHG) offers a compact source of ultrashort light pulses.
• Tailoring HHG polarization and photon energy is crucial for advanced applications.
• Extending the energy range of circularly polarized HHG is a key research frontier.

Purpose of the Study:

• To extend the photon energy range of circularly polarized high-harmonics.
• To generate single-helicity high-harmonic generation (HHG) spectra.
• To enable dynamic HHG chiral spectro-microscopies beyond the carbon K edge.

Main Methods:

• Utilized counter-rotating femtosecond laser pulses at 0.8 µm and 2.0 μm.
• Drove high-harmonic generation in helium and argon media.
• Theoretically analyzed the extension of photon energies beyond the carbon K edge.

Main Results:

• Achieved circularly polarized soft x-ray harmonics exceeding 170 eV in helium.
• Generated dense, single-helicity HHG spectra in argon well beyond the Cooper minimum.
• Demonstrated theoretical potential for extending circularly polarized HHG beyond the carbon K edge.

Conclusions:

• The dual-color laser approach significantly extends the achievable photon energy for circularly polarized HHG.
• Single-helicity HHG spectra were generated, consistent with attosecond pulse trains.
• This advancement broadens the scope of molecular and materials systems accessible to dynamic HHG chiral spectro-microscopies.